This paper presents a numerical study of the Reynolds
number and scaling effects in microchannel flows. The configuration
includes a rectangular, high-aspect ratio microchannel with heat
sinks, similar to an experimental setup. Water at ambient
temperature is used as a coolant fluid and the source of heating is
introduced via electronic cartridges in the solids. Two channel
heights, measuring 0.3 mm and 1 mm are considered at first. The
Reynolds number varies in a range of 500–2200, based on the
hydraulic diameter. Simulations are focused on the Reynolds number
and channel height effects on the Nusselt number. It is found that
the Reynolds number has noticeable influences on the local Nusselt
number distributions, which are in agreement with other studies. The
numerical predictions of the dimensionless temperature of the fluid
agree fairly well with experimental measurements; however the
dimensionless temperature of the solid does exhibit a significant
discrepancy near the channel exit, similar to those reported by
other researchers. The present study demonstrates that there is a
significant scaling effect at small channel height, typically ≤0.3 mm, in agreement with experimental observations. This scaling
effect has been confirmed by three additional simulations being
carried out at channel heights of 0.24 mm, 0.14 mm and 0.1 mm,
respectively. A correlation between the channel height and the
normalized Nusselt number is thus proposed, which agrees well with
results presented.